An exhaust gas purifier utilizing a catalyst is one of the conventional means for eliminating carbon monoxide, unburnt hydrocarbons and nitrogen oxides which are said to be the most harmful gases contained in the emissions of internal combustion engines.
Among the exhaust gas purifiers of this catalyst type, the most common one holds layers of catalyst pellets, i.e., pellets carrying a metallic catalyst enclosed in a metal casing. The exhaust gas, as it passes through such layers of catalyst pellets, is rendered harmless by chemical reaction.
Another type of exhaust gas purifier uses an integrated catalyst, as illustrated by U.S. Pat. Nos. 3,441,381 and 3,441,382. In this type both ends are open and the purifier holds a metallic catalyst carried by a ceramic carrier with a plurality of internal passages for exhaust gas.
Exhaust gas purifiers of the last-mentioned integrated catalyst type are superior to those of the pellet catalyst type in that the catalyst does not deteriorate as a consequence of abrasion during vibration and the catalyst vessel itself is simplified in structure.
When the integrated catalyst is installed within a cylindrical vessel, however, a space is usually left between the inner wall of the cylindrical vessel and the outer wall of the integrated catalyst under high temperature on account of the wide difference between the rate of thermal expansion of the metallic vessel and that of the integrated catalyst, which is ceramic. Since this space is quite wide, a violent impact occurs between the vessel and the catalyst due to vibrations transmitted from the engine, unless cushioning means is provided between the vessel and the catalyst; and this results in destruction of the integrated catalyst.
To prevent this, according to U.S. Pat. No. 3,441,381, the space between the inner wall of the vessel and the outer wall of the integrated catalyst is filled with metal textile, which serves as a cushioning means; and according to U.S. Pat. No. 3,441,382, the integrated catalyst is held in position by springs with ceramic heat insulation provided between them.
In the case of the above-mentioned metal textile, this textile would make an effective cushioning material if its elasticity were not lost at high temperatures in practical service; but when installed on an automobile with wide variations of load, it is exposed to a temperature of several hundred .degree.C under high load engine operation. At such high temperatures it loses its elasticity and ceases to be effective for cushioning. Consequently the catalyst is often broken.
When springs are used to hold the catalyst in position, the construction is complicated and the manufacture is not easy, resulting in a high cost of manufacture. It is also possible to mount the integrated catalyst in the vessel by shrink-fitting; but this method is not advisable, because it requires high precision in the external dimensions of catalyst and the internal dimensions of vessel, resulting in a poor yield and a very high cost.